Obesity is highly prevalent and problematic among the US obstetric population, necessitating the development of novel interventions to simultaneously address the associated health risks for both mother and child. The long-term objective of this study is to reduce risk for obesity-related health conditions during and after pregnancy among overweight/obese mothers and their infants. We have developed an innovative, theoretically-driven 10-session intervention to be delivered during pregnancy, which aims to (1) limit gestational weight gain, (2) increase uptake of gestational diabetes (GDM) screening, and (3) promote maintenance of exclusive breastfeeding. The intervention will be integrated into an existing, midwife-delivered model of group prenatal care (GPNC): CenteringPregnancy and piloted among pregnant women (n=80) in American Samoa. Specific aims are to: (1) determine the feasibility and acceptability of the GPNC intervention by measuring group attendance, attrition, and collecting quantitative and qualitative measures of feasibility and acceptability; and (2) to demonstrate the preliminary efficacy of the intervention by examining gestational weight gain, uptake of GDM screening, and breastfeeding. In a randomized controlled design, overweight/ obese women will be randomly assigned to the GPNC intervention (n=40) or individual standard of care (n=40). We hypothesize that the intervention will result in reductions in the proportion of women exceeding Institute of Medicine gestational weight gain guidelines, improvements in the uptake of GDM screening and longer maintenance of exclusive breastfeeding. We will explore processes underlying any positive intervention outcomes by measuring pregnancy knowledge, self-efficacy, social support (foundations of the social cognitive theory underlying the intervention), and the adoption of healthful dietary and physical activity behaviors. Existing interventions to promote the adoption of healthful behaviors in pregnancy and the early postpartum period have had limited success, particularly among low-income, ethnic minority groups who are most at risk of entering pregnancy overweight/obese and experiencing poor pregnancy outcomes. Our intervention design is responsive to key barriers faced by overweight/obese low-income populations and will be tested in a population not only in critical need (86% of American Samoan women are overweight or obese when they become pregnant versus ~42% of the general US population) but characteristic of other low- income, low-health literacy groups across the US. Integrating a theoretically-driven intervention, tailored for low-income, overweight participants, into prenatal care presents a promising opportunity to provide sustainable care and impactful health promotion. Targeting this high risk population means this study is poised to have significant public health impact and the use of an existing, widely-used, insurance-supported prenatal care curriculum offers high potential for future scalability.